'\" t
.TH "SD_BUS_MESSAGE_GET_MONOTONIC_USEC" "3" "" "systemd 257" "sd_bus_message_get_monotonic_usec"
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.SH "NAME"
sd_bus_message_get_monotonic_usec, sd_bus_message_get_realtime_usec, sd_bus_message_get_seqnum \- Retrieve the sender timestamps and sequence number of a message
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_message_get_monotonic_usec('u
.BI "int sd_bus_message_get_monotonic_usec(sd_bus_message\ *" "message" ", uint64_t\ *" "usec" ");"
.HP \w'int\ sd_bus_message_get_realtime_usec('u
.BI "int sd_bus_message_get_realtime_usec(sd_bus_message\ *" "message" ", uint64_t\ *" "usec" ");"
.HP \w'int\ sd_bus_message_get_seqnum('u
.BI "int sd_bus_message_get_seqnum(sd_bus_message\ *" "message" ", uint64_t\ *" "seqnum" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_message_get_monotonic_usec()\fR
returns the monotonic timestamp of the time the message was sent\&. This value is in microseconds since the
\fBCLOCK_MONOTONIC\fR
epoch, see
\fBclock_gettime\fR(2)
for details\&.
.PP
Similarly,
\fBsd_bus_message_get_realtime_usec()\fR
returns the realtime (wallclock) timestamp of the time the message was sent\&. This value is in microseconds since Jan 1st, 1970, i\&.e\&. in the
\fBCLOCK_REALTIME\fR
clock\&.
.PP
\fBsd_bus_message_get_seqnum()\fR
returns the kernel\-assigned sequence number of the message\&. The kernel assigns a global, monotonically increasing sequence number to all messages transmitted on the local system, at the time the message was sent\&. This sequence number is useful for determining message send order, even across different buses of the local system\&. The sequence number combined with the boot ID of the system (as returned by
\fBsd_id128_get_boot\fR(3)) is a suitable globally unique identifier for bus messages\&.
.PP
Note that the sending order and receiving order of messages might differ, in particular for broadcast messages\&. This means that the sequence number and the timestamps of messages a client reads are not necessarily monotonically increasing\&.
.PP
These timestamps and the sequence number are attached to each message by the kernel and cannot be manipulated by the sender\&.
.PP
Note that these timestamps are only available on some bus transports, and only after support for them has been negotiated with the
\fBsd_bus_negotiate_timestamp\fR(3)
call\&.
.SH "RETURN VALUE"
.PP
On success, these calls return 0 or a positive integer\&. On failure, these calls return a negative errno\-style error code\&.
.PP
On success, the timestamp or sequence number is returned in the specified 64\-bit unsigned integer variable\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
A specified parameter is invalid\&.
.RE
.PP
\fB\-ENODATA\fR
.RS 4
No timestamp or sequence number information is attached to the passed message\&. This error is returned if the underlying transport does not support timestamping or assigning of sequence numbers, or if this feature has not been negotiated with
\fBsd_bus_negotiate_timestamp\fR(3)\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_bus_message_get_monotonic_usec()\fR,
\fBsd_bus_message_get_realtime_usec()\fR, and
\fBsd_bus_message_get_seqnum()\fR
were added in version 209\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_new\fR(3), \fBsd_bus_negotiate_timestamp\fR(3), \fBclock_gettime\fR(2), \fBsd_id128_get_boot\fR(3)
